Known friction clutches provide a releasable torsional connection between a motor vehicle engine flywheel and an associated transmission. Repeated clutch disengagement and engagement cycles wear the friction material of the clutch driven disc. If the clutch is allowed to slip excessively, or is abused, an undesirable amount of heat may be generated heat within the clutch. The heat has the potential to affect the engagement characteristics of the clutch and also to increase the wear rate of the friction material. Excess heat build-up in the pressure plate can result in a deterioration in clutch performance. Excess heat is preferably absorbed and dissipated by the clutch. Some clutch pressure plates have cooling fins to facilitate the dissipation of heat in the pressure plate. However, in some cases, the cooling fins are inadequate to dissipate the heat rapidly enough. The cooling fins may also be unable to sufficiently reduce variations in thermal distribution throughout the pressure plate to reduce the generation of thermal stress.
The above mentioned wear of friction material is also a concern. As the friction material wears, the clutch clamping load generated by a spring acting directly or indirectly against the pressure plate tends to decrease. Clutches are commonly provided with adjustment mechanisms to compensate for wear of the friction material and the attendant loss of clamping load. However, adjustment mechanisms, particularly certain types of automatic adjustment mechanisms, occupy or interfere with the location of cooling fins on the pressure plate. Therefore, clutches are generally equipped with cooling fins or with an automatic adjustment mechanism, but not both.
It is desired to provide a means of cooling the clutch pressure plate which is both effective at cooling the pressure plate and will accommodate an automatic adjustment mechanism.
It is also desired to provide a feature on the pressure plate which dissipates heat from a pressure plate more effectively than cooling fins.